1. Field of the Invention
The present invention relates to a recording/reading apparatus and a suction device that can be effectively used therein. The present invention is satisfactorily applicable, for example, to a sheet feeding device for feeding sheets to an image recording apparatus, an image reading apparatus or the like. Further, the present invention is applicable to a recording/reading apparatus that records images on sheets fed by such a feeding device or reads images from the sheets.
2. Description of the Related Art
Sheet feeding devices have been used in various apparatuses including image recording apparatuses and image reading apparatuses. There are various known structures and mechanisms of such sheet feeding devices. There are various types of means for realizing the function of a sheet feeding device by which sheets can be extracted one by one from a number of sheets stacked together. In many cases in which sheets of paper are to be fed, rubber rollers are used to extract the sheets one by one. When the sheets consist of films, static electricity is liable to be generated due to the smaller degree of surface roughness as compared with that of paper sheets, with the result that the sheets that are stacked together are attracted to each other by a greater force. In view of this, a suction cup is often used. By reducing the inner pressure of the suction cup, sheets can be taken one by one off the pile.
FIG. 1 schematically shows the construction of a device for reducing the inner pressure of a suction cup to pick up sheets by suction. In FIG. 1, numeral 81 indicates a suction cup having a hole 81a formed for the purpose of expelling air from the suction cup. This hole is connected to a hose 82a. The other end of the hose 82a is joined to an electromagnetic valve 83. The other end of the electromagnetic valve 83 is connected to an electromagnetic pump 84 through a hose 82b. A diaphragm 85 that is made of rubber, shown in FIG. 2, is provided inside the electromagnetic pump 84. The diaphragm 85 has a central portion 85a which is repeatedly moved back and forth at high speed by an electromagnetic force generating means (not shown). The diaphragm 85 is fitted onto a base 86, which has an air inlet hole 86a, an air outlet hole 86b, and one-way valves 87 and 88. The hose 82b is connected to the air inlet hole 86a of the diaphragm 85 inside the electromagnetic pump 84. Thus, the gas drawn in through the air inlet hole 86a as a result of the back-and-forth movement of the diaphragm 85 is expelled through the air outlet hole 86b, whereby the pressure in the device portion that is connected to the air inlet hole 86a can be reduced.
In the above-described construction, when a sheet is to be picked up by suction, the suction cup 81 is pressed against the sheet, and the electromagnetic valve 83 is closed. Then, the electromagnetic pump 84 is operated. The operation of the electromagnetic pump 84 is continued throughout the sucking up of the sheet. When the sucking action is to be cancelled, the electromagnetic valve 83 is opened, and the electromagnetic pump 84 is stopped. The reason for using an electromagnetic valve is to draw in air quickly to thereby speedily cancel the sucking action.
Apart from the diaphragm type electromagnetic type shown in the drawing, there are various other types of electromagnetic pumps applicable. In some cases, a centrifugal pump as shown in FIG. 3 is used. In FIG. 3, numeral 90 indicates an impeller, and numeral 89 indicates a body having an air inlet hole 89a and an air outlet hole 89b.
According to a known method, a sheet can be picked up by suction by using an air cylinder as shown in FIG. 4, (Japanese Patent Laid-Open No. 60-118550). According to another known method, a suction cup is first deformed and then restored to its original shape by a restoring force of the suction cup itself, as shown in FIG. 5, whereby a sheet can be picked up. In FIG. 4, numeral 91 indicates an outer cylinder to which a hose 93 is joined. Numeral 92 indicates an inner cylinder which can be moved to the right and left (as seen in the drawing) to thereby increase and decrease the volume of the interior while keeping the interior airtight with respect to the inner wall of the outer cylinder 91. A suction cup is joined to the forward end of the hose 93 and pressed against a sheet. In this condition, when the inner cylinder 92 is pulled, the pressure of the interior is reduced, thereby enabling the sheet to be picked up by suction. In the case of FIG. 5, a suction cup 94 having no air outlet hole is used. When the suction cup 94 is pressed against a sheet, a cone-shaped section 94a of the suction cup 94 is deformed, and, due to the restoring force of this deformed section 94a, a reduction in the pressure of the interior of the suction cup 94 occurs to thereby pick up the sheet by suction.
The above-described conventional mechanisms, however, have the following problems:
1. Since the electromagnetic pump continues to be driven while the sheet is being picked up by suction, a noise continues to be generated from the pump, so that the device is rather noisy. PA1 2. Since the electromagnetic pump continues to be driven while the sheet is being picked up by suction, a vibration continues to be generated from the pump, thereby causing a deterioration in the performance of the device. On the other hand, provision of a vibration isolator would result in an increase in cost. PA1 3. The electromagnetic valve and the electromagnetic pump are rather expensive and lead to a rather high cost. PA1 4. When a rubber member of low durability is used in the movable section of the electromagnetic pump, a periodical replacement of this rubber member is required, resulting in an increase in running cost. PA1 5. In the case of the cylinder type device, it is necessary to maintain the requisite airtightness in the slide section, which means this type of device involves problems in terms of manufacturing precision and durability. PA1 6. In the type of device utilizing the deformation of the suction cup, no good method is available for cancelling the sucking action.